what is a "case file"?
Is that a record in a FileMaker table?
If so, there is no way to undelete a record short of opening a back up copy of the database file that has not had the record deleted.
Some Developers set up a system to "mark" a record as "deleted" and design their layouts to hide deleted records from view. Then they can "undelete" file by clearing the field that marked it as a deleted record.